Page "Psionics (Dungeons & Dragons)" Paragraph 17

The psionics system was greatly revised in Player's Option: Skills & Powers and the revised Dark Sun Campaign Setting.

The system was redevised around a Mental Armor Class ( MAC ) and a Mental THAC0 ( MTHAC0 ), mimicking the Armor Class ( AC ) and THAC0 used in normal combat.

The harder the power was to use, the lower the MAC was to activate it.

Likewise, the harder a mind was to break into, the lower that person's MAC was.

Psionicists would have MTHAC0 scores that represent their ability to wield the psionic arts.

This was exactly 21 minus the level of the psionicist.

Many of the powers were also altered in this revision.